The manufacturing process of aluminum results in a toxic and highly alkaline by-product, red mud. The chemical composition of red mud varies based on the applied conditions during the production of aluminum. However, hematite (α-Fe 2 O 3 ), goethite (α-FeOOH), boehmite (γ-AlO(OH)), and quartz (SiO 2 ) are the major compounds and calcite (CaCO 3 ) and gibbsite (Al(OH) 3 ) are the minor compounds that constitute in the raw red mud. The characteristic studies conclude that red mud reacting with water molecules releases OHions contributing to high pH. With suitable treatment methods, red mud can be converted into cementitious material and used in the construction industry [1]. As per the studies, red mud calcined

A novel binder system for cement-based composites depending upon the strength and durability characteristics is introduced in this study. The possibility of calcined red mud cement pastes with and without colloidal nano-silica (CNS) over Ordinary Portland Cement paste (OPC) at three W/B ratios (0.3, 0.4, 0.5) is evaluated. The optimum percentage of cement replacement by red mud (15%) was selected from compressive strength values of different cement replacements (5%, 10%, 15%, and 20%). Colloidal nano-silica (CNS) was added at 0.5%, 1%, 1.5%, and 2 % to the selected red mud cement paste. Water absorption, sorptivity, resistance to sulfate attack, and resistance to acid attack tests were conducted for optimum red mud cement paste with and without CNS. The experimental results are explained based on tortuosity with empirical formulas and mathematical models of pore network distribution. The tortuosity is directly proportional to the inter-connectivity of the pores. The mixes with 15% calcined red mud and 1.5% CNS replacement performed better strength and durability at all W/B ratios. The mix (R15NS1.5) with minimum tortuosity value results in the higher overall performance of the paste. The mixes with a 0.3 W/B ratio give high-performance cement paste compared to higher W/B ratios.